Women constitute nearly half of the 33 million HIV-1-infected individuals in the world and the vast majority acquire this infection heterosexually. Multiple lines of evidence suggest that female sex hormones alter susceptibility of HIV-1 (HIV) as well as disease progression, but mechanisms underlying this are unknown. Expression ofthe HIV coreceptor, CCR5, and its ligands, the B-chemokines, has been strongly linked to HIV susceptibility and disease progression, however their relative importance in vivo is controversial. Preliminary data from our and other laboratories suggest that estrogen (E) and progesterone (P) alter expression of CCR5 and its ligands in whole blood (WB) and the female genital tract. Specifically, E upregulates CCR5 and its ligands, whereas P downregulates them. We hypothesize that both E and P modulate CCR5 and one of its most important and abundant ligands, CCL5, but changes in CCL5 predominate. In the proposed studies, the influence of E and P on HIV coreceptors and their ligands will be determined by studying three cohorts of women before and after hormonal therapy: reproductive-age women who undergo gonadotrophin-releasing hormone agonist-induced sex hormone suppression randomized to E or placebo for 3 months then P for 2 weeks in the third month; postmenopausal women randomized to E or placebo for 4 weeks followed by E+P for 12 days; and HIV seropositive postmenopausal women who receive E for 4 weeks followed by E+P for 12 days. CCR5 and CXCR4 density will be determined by flow cytometric analysis of whole blood and cervical CD4+ T cells; inducible and constitutive p-chemokine and CXCL12 production will be measured in whole blood and cervical lavage specimens by ELISA; PBMC CCR5, CXCR4, and CCL5 mRNA will be determined by RT PCR; and, in HiV seropositive women, plasma and genital tract viral load will be measured. Knowledge of the influence of physiologic levels of E, P and aging on HIV chemokine coreceptors, their ligands, and genital tract viral load could provide mechanistic insight into the biology of HIV transmission and disease progression in women. Ultimately, this information is needed to develop rational standard practices of prescribing hormonal therapies to HIV infected women at all stages of life.